In the art, prior to machining of a thin-walled workpiece (for example, an aerospace thin-walled blade), a simple-structured fixture or screws are usually applied to position tightly the thin-walled workpiece on a machine platform. Referring to FIG. 6, two conventional clamping devices 90 are applied to clamp individually at two opposing ends of a workpiece 20, in which each the clamping device 90 is consisted of a base structure 92 and a cover plate 91. Both the base structure 92 and the cover plate 91 are made of metallic materials. After this assembly as shown in FIG. 6 is sent for machining or milling at both sides thereof, the final thin-walled product of the workpiece 20 is shown in dashed lines.
While in milling or machining a coarse embryo or a medium embryo, a larger portion of material would be removed, and also a demand in efficient machining is always true at this stage. Thus, vibrations resulted from the machining would be significant, especially at a process of machining the workpiece thinner and thinner, from which stiffness of the workpiece would become too low to sustain vibrations or shaking. Namely, as a steady-state domain for the machining becomes restricted and smaller, choices upon machining parameters for maintaining the machining within the steady-state domain would be extremely limited. Thereupon, work efficiency of the machining would be poor. Hence, to prevent the machining of the workpiece from less accuracy and a lower yield due to machining perturbations, the vibrations induced during the machining shall be damped, and also the machining shall be processed in a steady state.
In the art, a conventional shock absorber or damper for the workpiece is usually hung exterior to or contacted with the workpiece, and is generally performed by a spring. It is understood that such a design can only damp the vibration within a limited frequency range (i.e., for a single vibration mode). However, for a thin-walled workpiece, it is quite possible that more than one natural frequency (corresponding to different mode shapes) for the thin-walled workpiece may exist around the work frequency of the machining. Thus, under such a circumstance, vibrations related to the rest of modes, other than the one to which the damper is targeted, will be merely affected by the damper.
In addition, a conventional fixture with a damping ability is usually able to damp the vibration in a unique direction. However, since the mode shape of the workpiece may be three-dimensional, thus a stress analysis shall be performed in advance to locate the position of the maximum shearing stress, such that a damping means can then be appropriately applied to restrain the corresponding mode shape.
Accordingly, a topic of finding a fixture for a thin-walled workpiece that can provide an inclined shock-absorbing surface for multi-dimensional vibration modes is definitely urgent for damping most of the vibration modes of the thin-walled workpiece during the machining, and for assuring the machining to be operated around a steady state.